1. Field of the Invention
The present invention relates to failure diagnosis in a vehicle such as an automobile and, more specifically to collecting information about abnormalities.
2. Description of the Related Art
An electronic control unit (ECU) mounted in a vehicle can continuously execute self-diagnosis and, when a failure or an abnormality is detected, abnormality information such as a so-called diagnostic trouble code (DTC) representing the contents of the failure, and the year, month, day, and time instant or time-instant information can be stored in a storage means as described, for example, in JP-A-7-181112.
In failure diagnosis processing in such an ECU, decision processing associated with deciding whether an abnormality has occurred is regularly executed. The occurrence of an abnormality is confirmed for the first time when an abnormality confirmation time is reached during decision processing. Waiting until an abnormality confirmation time before confirming the occurrence of an abnormality is intended to prevent erroneous detection. When the abnormality is confirmed, abnormality information is then stored.
It should be noted that many modern vehicles have adopted a form of an onboard control network having multiple ECUs interconnected over a communication line, along with the capability for great diversity and complexity in the contents of the control afforded by such a network.
In the onboard network, the multiple ECUs control respective objects while transferring and exchanging control information. When triggered for example by an abnormality in a certain region, abnormalities whose contents are different from each other may be detected in multiple ECUs at the same time.
For example, when a pulsating crank angle sensor signal is inputted to an first ECU of two ECUs that cooperate with each other in controlling an engine, the first ECU transmits engine speed information, which is detected based on the crank angle sensor signal, to the second ECU whereupon the second ECU uses the engine speed information to execute processing. In a case where imperfect contact occurs on signal line extending from the crank angle sensor to the first ECU, an abnormality in the crank angle sensor will be registered if the crank angle sensor signal loses a pulse. Moreover, the engine speed information sent from the first ECU to the second ECU can undergo a larger fluctuation than normal due to the lost pulse. Based on the fluctuation, the second ECU decides that an imperfect ignition condition exists and thus detects a misfire abnormality.
Even within one ECU, abnormalities whose contents are different from each other may be detected at the same time upon being triggered with an abnormality in a certain region. For example, an ECU that executes control processing using signal sent from a sensor while feeding power from a built-in power circuit to the sensor can detect multiple abnormalities triggered by an abnormality. Assuming that an output abnormality occurs in the power circuit for the sensor, a sensor power abnormality is detected through processing of monitoring an output of the power circuit. Moreover, a sensor abnormality is also detected through processing of monitoring a sensor signal since the power abnormality will prevent a normal sensor output.
According to the related art, when occurrence of an abnormality is confirmed, time-instant information is stored together with abnormality information. If multiple abnormalities are detected in multiple ECUs or one ECU, the sequence in which individual abnormality information associated with the respective abnormalities are confirmed and stored can be learned by reading the abnormality information and the time-instant information.
However, an abnormality confirmation time varies depending on the detection processing of each abnormality. If different abnormalities are detected upon being triggered by an abnormality in a certain region, one abnormality may be confirmed earlier than an other abnormality based on detection processing even though the other abnormality actually occurred earlier. That is, an erroneous ordering of an abnormality detection sequence may occur.
In the related art, since time-instant information associated with when the time of occurrence of an abnormality is confirmed is stored, the phenomenon of erroneous ordering cannot be detected. Further, because of the erroneous ordering, it is not readily possibly to find an abnormality that has triggered detection of multiple abnormalities.
For example, in the case of the two ECUs, assuming that a time when a decision regarding a crank angle sensor abnormality is confirmed in the first ECU is set after a time when a decision regarding a misfire abnormality is confirmed in the second ECU, even though the abnormality in the crank angle sensor has triggered the misfire abnormality, the misfire abnormality information may be stored in the second ECU earlier than the information associated with the crank angle sensor abnormality is stored in the first ECU through various differences in the detection processing. Consequently, the time-instant information stored together with the abnormality information demonstrates that the misfire abnormality has occurred earlier than the abnormality in the crank angle sensor. In such a case, the real cause of an abnormality or failure cannot be discovered.